Which of the following can produce fertile hybrids in captivity?

Options

A. Panthera leo and Panthera tigris
B. Mallard and the Pintail Duck
C. Polar bear and Alaskan brown bear
D. All of these

Answer

To determine which of the following can produce fertile hybrids in captivity, we need to analyze each option provided in the question.

1. **Panthera Leo (Lion) and Panthera Tigris (Tiger)**:
- Lions and tigers can interbreed in captivity, producing hybrids known as ligers (lion-tiger hybrids). These ligers are capable of reproducing with other ligers, which means they are fertile.

2. **Mallard Duck and Pintail Duck**:
- The Mallard is a wild duck, and the Pintail is another species of duck. While these two species do not typically breed in the wild due to ethological isolation (behavioral differences), they can produce fertile offspring when bred in captivity.

3. **Polar Bear and Alaskan Brown Bear**:
- Polar bears and Alaskan brown bears can also interbreed and produce hybrids known as "pizzly" or "grolar" bears. These hybrids are fertile and can reproduce.

4. **All of the Above**:
- Since all the pairs mentioned (lions and tigers, mallard and pintail ducks, polar bears and Alaskan brown bears) can produce fertile hybrids in captivity, the correct answer is option D: all can produce fertile hybrids in captivity.

### Final Answer:
**D. All of these**